The present invention relates to a foldable and collapsible, concavely curved antenna reflector having, when deployed, a very highly accurate contour in terms of geometric contour and feature requirements, and being made of uniform rigid segments hingedly connected to a central panel.
Antenna reflectors are, for example, constructed from carbon fibre re-enforced, synthetic material (CFK); this kind of material is used particularly to construct rigid antenna reflectors. Such a material permits satisfying the requirements for space technology and involving contour accuracy and, therefore, high performance antenna systems. Power and performance of such antenna are, however, limited owing to the size, dimensions, etc. of the payload space in a carrier space vehicle. Completely rigid antennas are highly impractical in space hence the requirements for practical purposes can be satisfied only when the antenna is of a collapsible and foldable construction, i.e. can be launched compactly folded to be unfolded and deployed after launching. Particularly, such antennas are folded down and moved by the carrier vehicle into an orbit, for example, and, once in orbit the antenna is deployed using an appropriate deployment mechanism.
Basically, antenna reflectors of the collapssible and foldable variety come in two versions, and, in fact, it is believed that only these two alternatives are available for space use. Owing particularly to the requirement of the high contour accuracy. One of the types is a grid or mesh type of reflector which, however, was also found to be unsatisfactory as far as contour accuracy is concerned, so that actually only one type of reflector remains, namely the type to which the invention pertains, including foldable rigid and hinged segments. Reflectors with these foldable rigid segments come in a variety of different configurations, however, some of these configurations are disadvantaged by the requirement for an excessive number of joints and segment pieces which, owing to the particular folding and collapsing construction, are of different shape and size. Also, the larger the number of hinges and segments, the more complex will be the deployment mechanism and its operation. The deployment mechanism must, in addition, be constructed to orient the various panels or segments in relation to each other which, or course, is again a task whose complexity increases with the number of panels involved. Unfortunately, it has not been possible to reinforce the panels and segments through ribs, lattice structure or the like, owing to the lack of storage space in the carrier vehicle. On the other hand, it is clear that the larger such an antenna, the greater is the need for stiffening and re-enforcing elements simply to maintain the desired degree of accuracy.
Antenna reflectors of the type referred to above are generally known, for example, through U.S. Pat. Nos. 3,699,576 and 3,715,760. These patents indeed show central panel and single axes joints and hinges for pivotally mounting these various segments or panels to that central panel. In the first patent, the segments are, to some extent, supported and re-enforced through a small lattice structure in the rear. In both instances, there is an interconnection of the various segments through hinges, which support and permit the folding and unfolding of the various segments. A similar configuration is, for example, shown in the NASA-Conference Publication 2118, of November, 1979, and described by J. S. Archer under "Advanced Sunflower Antenna Concept Development". Aside from the relatively large construction and expenditure needed here, there is an added weight problem, but the primary disadvantage of the structure is the large number of hinges which, on one hand, are necessary for finally attaining the desired contour accuracy, but as far as the deployment procedure is concerned, these hinges are troublesome.
German printed patent application No. 31 28 978 shows a foldable radiation reflector of rotational symmetry, having a plurality of segments arranged around the axis of symmetry and being pivotally connected to the requisite support structure. Upon folding down, the segments have a particular position of deployment, and they are now being turned in the same direction and in the same manner, about the respective turning axis being associated with each panel and extending parallel to the aforementioned axis of symmetry, while simultaneously they pivot up. This way the panels are folded down. For purposes of deployment, the aforementioned motions are directly reversed whereby particularly each panel will undergo again a simultaneous turning and pivot motion. This method of deployment as disclosed, is disadvantaged by the fact that deployment and folding down requires a rather complex turning and pivot mechanism whose complexity, to some extent, interferes with the accuracy of the antenna once deployed. Stiffening of the segments in relation to the central and stationary reflector part, is very difficult.
Another proposal has been made in "SCI" (83) 1, pages 7 through 16, and 63 through 66, for the FIRST satellite, involving particularly an antenna construction of the folded variety. The segments are preferably arranged on the central segment, and they are also interconnected to each other through hinges. Folding and deployment of the segments is carried out in a single axis operation, through radial pivoting of the segments without turning. This reduces the complexity of the pivot mechanism, and acutally increases the accuracy of the deployed shape. However, it was found that this particular antenna is highly disadvantaged by an ineffective utilization of the available storage room and poor possibility of additional stiffening. Moreover, owing to the segment position when folded down, the various hinges and segments have different dimensions.
In accordance with U.S. Pat. No. 4,511,901, a foldable antenna reflector is known wherein hinged joints of the outer ends of juxtaposed segments are provided through connecting rods being attached towards the middle of the outer end of a segment. The joint connecting the segments with a central panel is of a two-axis construction similar to German patent application No. 31 28 978. A drive acts on this two-axis hinge for purposes of deployment of the reflector such that the segments will pivot radially outwardly. The accuracy attainable with this reflector is very high, but the position of accuracy is supported by expensive and very complex mechanical means. Moreover, guide rods on the head end of the segments are necessary for synchronizing the in-turning motion and for attaining the requisite contour accuracy.